This invention relates to a method of preparing 1,1,1-trifluoro-2,2-dichloroethane CF.sub.3 CHCl.sub.2 from 1,1,1-trifluoro-2,2,2-trichloroethane.
1,1,1-Trifluoro-2,2-dichloroethane (will be referred to as fluorocarbon 123) can be fluorinated into CF.sub.3 CHClF (fluorocarbon 124) which is useful as a working fluid or can be oxidized and hydrolyzed into trifluoroacetic acid. Furthermore, fluorocarbon 123 is expected to serve as a substitute for fluorocarbon 11 which is used as a foaming agent for polyurethane resins.
According to J. Fluorine Chem., 13, 7-18 (1979), CF.sub.3 CHCl.sub.2 is obtained by fluorinating tetrachloroethylene with hydrogen fluoride in the presence of a metal halide catalyst, but by this method the yield of CF.sub.3 CHCl.sub.2 is very low.
Also it is known that CF.sub.3 CHCl.sub.2 can be derived from 1,1,1-trifluoro-2,2,2-trichloroethane. USP 4,145,368 shows preparing CF.sub.3 CHCl.sub.2 by subjecting CF.sub.3 CCl.sub.3 (fluorocarbon 113a) and CF.sub.3 CH.sub.2 Cl (fluorocarbon 133a) to a disproportionation reaction on a chromium oxide catalyst, but the reported yield of CF.sub.3 CHCl.sub.2 is only about 14%. JP-A 58-222038 shows that CF.sub.3 CHCl.sub.2 is obtained at good yield by reduction of CF.sub.3 CCl.sub.3 with zinc dust in a protic solvent. However, this method is inconvenient for industrial adoption because the disposal of by-produced zinc chloride and unreacted zinc dust is not easy and also because distillation is necessary for separating CF.sub.3 CHCl.sub.2 from the protic solvent.